1. Field of the Invention
This invention relates to waveguides. Particularly, this invention relates to radio frequency (RF) radiation transmission in rectangular waveguides such as may be employed in phased array antennas.
2. Description of the Related Art
A well understood transmission media of RF electromagnetic energy is the rectangular waveguide. The rectangular waveguide supports an infinite number of electromagnetic field patterns, or modes, in which the dominant field mode (TE10) is the most commonly used. The physical realization of the TE10 mode is a consequence of the geometry of the rectangular waveguide. The mode title, TE10, is a description of the field pattern; TE indicates that the E field component of the field pattern is always transverse (T) to the XY plane while the H field component may be either transverse or normal to the XY plane.
FIGS. 1A and 1B illustrate a TE10 wave excited in a rectangular waveguide using either an E field probe or an H field probe, respectively. As shown in FIG. 1A, an E field probe 102 is inserted into the waveguide 100 through the broad wall 104 of the waveguide 100 tangential (or parallel) to the E Field and is easily realizable with a coaxial cable where the coaxial shield 106 is grounded to the broad wall 104 of the waveguide 100 while the center probe 108 continues into the waveguide a determined distance. As shown in FIG. 1B, an H field probe 122 is inserted into the waveguide 120 through the narrow wall 124 and may be realized by looping the exposed center conductor 126 of a coaxial cable a determined length and attaching its end to the waveguide's broad wall 128 while the coaxial shield 130 is grounded to the narrow wall 124 of the waveguide 120. The loop of the H field probe 122 must be oriented such that the H field 132 is generated normal to the plane of the loop. Typically, an E field probe 102 will have a wider bandwidth than an H field probe 122. While an E field probe 102 is easier to manufacture and is the preferred method of exciting and launching a waveguide mode, an E field probe inserted into the narrow wall of a rectangular waveguide will not excite the dominant field pattern because it is orthogonal to the E field of the dominant mode. In both FIGS. 1A and 1B, the direction of propagation is along the z axis as shown.
Distribution networks that distribute power between a single input and multiple outputs are commonly developed using rectangular waveguides machined into conductive plate. In such a conventional waveguide distribution network, it is often preferred that the broad wall of the rectangular waveguide face the top of the plate. For example, referring to FIG. 1A, a plate of metal in the X-Z plane having a defined thickness in the Y dimension would have channels machined into it's surface defining a particular waveguide distribution network architecture. The channels are then covered with a top (e.g., a metallic plate) and, if required, a bottom plate ensuring continuous conductive waveguide surfaces. This allows the dominant transmission mode to be excited with an E field probe inserted from the top of the plate as shown in FIG. 1A and allows the most convenient machining of the splitters, bends and hybrids that are commonly used components of the waveguide architecture. Probes may be installed from the top or bottom surfaces of the network structure.
When used in a phased array antenna, the required distance between waveguide transmission paths decreases as the operating frequency and scan angle increases. This is a consequence of the reduction in spacing between array modules at the antenna face that are fed by the waveguide distribution network. The broad wall of rectangular waveguide measures twice in length or greater than the narrow wall. Thus, phased array antennas operating in microwave frequencies with high scan angles typically require a much denser waveguide distribution network pattern.
In view of the foregoing, there is a need in the art for apparatuses and methods for providing waveguide cavity launches that are easily implemented with plate-fabricated waveguide distribution networks. Further, there is a need for such apparatuses and methods to support dense waveguide distribution network patterns such as those employed in phased array antenna for communication satellites. Particularly, there is a need for such systems and methods to allow an easily manufactured E field probes to be used entering the narrow wall plane of a waveguide structure. These and other needs are met by the present invention as detailed hereafter.